Posts about: "Fuel (All)" [Posts: 1005 Pages: 51]

Originally Posted by BugBear

Consider losing one engine on the Dream. If it is a generator that's failed let's say #2 . Do the electric fuel pumps lose power? Only in #2? Does the mechanical pump start feeding right away? If so, is there a lull? Are both engines fuel pumps supplied off one Gen?

See I think there was no simultaneous loss of both 1, 2.
The odds give me a migraine. I still wonder if TCMA knows the difference between parked, rolling, rotated brakes and stowed. Only parenthetically, it didn't do this

Originally Posted by BugBear

Difficult!? Maybe not. If very late the flaps were tagged stowed, and there was a simultaneous gear up command, with FlapDown command, the overload could have failed a GCS. Then it becomes a switching exercise. (Automatics).

Alarms Warnings Impacted EICAS, ETC. it happened long ago, but we know what happens when an engine driven generator quits ..first it bangs for awhile, then it burns itself up, then ...

Originally Posted by MaybeItIs

Thanks for answering the question I hadn't yet asked but wanted to confirm!

I'm still sticking with "Major Electrical Fault" as my most likely cause, and this adds to my suspicions.

As I understand it, the landing gear is raised / retracted by electric motor-driven hydraulic pump (pumps?). This/these would create a significant electrical load.

If the plane's multi-redundant electrical system has a fault which is intermittent (the worst kind of electrical issue to diagnose), and which causes the redundancy controls to go haywire (as there are, of course, electronic controls to detect failures and drive the switching over of primary and backup electrical supplies), then this fault could to triggered by a large load coming on-line. It could even be as simple as a high current cable lug not having been tightened when a part was being replaced at some stage. The relevant bolt might be only finger-tight. Enough to work 99.99% of the time between then and now... But a little bit more oxidation, and particularly, a bit more heat (it was a hot day), and suddenly, a fault.

Having worked in electronics for years, I know that semi-conductors (and lots of other components, especially capacitors [and batteries]) can also degrade instead of failing completely. Electro-static discharges are great for causing computer chips to die, or go meta-stable - meaning they can get all knotted up and cease working correctly - until they are powered off for a while. They can also degrade in a way that means they work normally a low temperatures, but don't above a certain temperature.

Anyway, there MUST be ways that the redundant power supplies can be brought down, simply because, to have a critical bus powered from a number of independent sources, there must be "controls" of some sort. I don't know how it's done in the 787, but that's where I'd be looking.

As there is a lot of discussion already about how the bogies are hanging the wrong way suggesting a started but failed retraction operation, and it's now confirmed that the retraction would normally have taken place at about the point where the flight went "pear shaped", I'm going to suggest that the two things are connected. More than that: I'll suggest that the Gear Up command triggered the fault that caused both engines to shut down in very short succession. Nothing the pilots did wrong, and no way they could have known and prevented it.

It's going to be difficult to prove though.

Originally Posted by ILS27LEFT

Best post until now in my view. We will find out very soon I think. Gear up command triggered the instant lack of fuel to both engines. I'm not sure on how the fuel flow is dependant on the power supplies on the 787 but I genuinely believe you are very very close to what might have happened here.

Originally Posted by MaybeItIs

Yes, thanks, I've seen a few comments to this effect, and I have to accept most of what you say. I understand that they have their own dedicated generators and local independent FADECs (or EECs), but I'm trying to use what I do know to attempt to figure this out. I know that there are Fuel Cutoff switches in the cockpit. Somehow, if switched to Off, these will cut off the fuel to the engines, "no matter what". Of course, even that's not true, as the Qantas A380 engine burst apparently (comment in this thread) showed.

Anyway, the thing I'm looking at is how the fuel cutoff switch function could have been activated in some other way. To me, it seems obvious that there are wires that run between the engine fuel shutoff valves and the cockpit / flight control panel (no doubt with relays etc in between). I don't know where those shutoff valves are located, but logic says they should be located in the fuselage, not out at the engines. I also don't know how those valves operate - are they solenoid valves or electro-mechanically driven? Nor do I know where the power to activate those valves comes from, but using my logic, if those valves close when powered off, such as solenoid valves typically do, then the power cannot exclusively come from the engine-dedicated generators. If it did, you'd never be able to start the engines so they could supply their own power to hold those valves open. So, there must be some power (appropriately) fed from the main aircraft control bus to activate those valves - if the rest of what I'm assuming is correct. Anyway, like I say, I don't know enough about the details at this point, but there are many more ways to activate or deactivate a circuit than by flicking a switch. Killing the relevant power supply, for example. A screwdriver across some contacts (for example), another. Shorting a wire to Chassis, maybe. Just trying to contribute what I can.

You raise another interesting point: "TCMA notwithstanding". Could you elaborate, please? What will happen if the TCMA system, which apparently also has some degree of engine control, loses power? The problem with interlinked circuits and systems is that sometimes, unexpected things can happen when events that were not considered actually happen. If one module, reporting to another, loses power or fails, sometimes it can "tell" the surviving module something that isn't true... My concern is where does the power to the Fuel Cutoff switches come from? Are there relays or solid-state switches (or what?) between the Panel Switches and the valves? If so, is the valve power derived from a different source, and if so, where? Are the valves solenoids, open when power applied, or something else? What is the logic involved, between switch and valve?

Would you mind answering these questions so I can ponder it all further, please? If I'm wrong, I'll happily say so.

Originally Posted by lucille

What\x92s the usual time frame for the release of preliminary data and report from the FDR and CVR? Is it around 6 months?

I guess if no directives come from Boeing or the FAA in the next 2 weeks, it can be presumed that a systems failure from which recovery was impossible was unlikely.

Originally Posted by bakutteh

Massive loss of lift misidentified as loss of thrust. If any one pilot just had a dual engine failure scenario on a recent sim ride, brain and muscle memory would jump to loss of thrust in dual engine, prompting them to accomplish the recall memory items which called for both engine fuel switches to OFF and then RUN, and physically deployed the RAT.

Originally Posted by fdr

If you are referring to loss of all boost pumps, am not aware of any engine that will not continue to run with a suction feed to the main boost pumps at low altitudes.

Originally Posted by Someone Somewhere

Gear and flaps are both hydraulic, and the hydraulic pumps typically act as effective fault-containment - a hydraulic failure or excess load doesn't result in excess demand on the electric side; the pump just starts to run out of output flow/pressure.

Originally Posted by Someone Somewhere

In addition, the 787 has four main generators and I believe the switching is segregated into at least two controllers, on top of the four separate generator control units.

Originally Posted by Someone Somewhere

And again, electrical failure should not cause engine failure - consider QF32 where the wiring to the engine was mostly severed and they had to drown it with a fire truck.

Originally Posted by Someone Somewhere

It's not. Boost pumps should be more-or-less unnecessary at sea level.

Originally Posted by Someone Somewhere

I believe the valves are almost all bi-stable power-open power-close. When not powered, they remain in the last commanded position.

The valves are located in the spar (hence being called 'spar valves'. The fuel tank is immediately above the engine so it is a very short pipe for suction feeding. Tail mount engines are potentially a different story...

Originally Posted by BrogulT

Is the ability of an engine to run using only suction feed ever actually checked or tested during operations or maintenance procedures?

Originally Posted by MaybeItIs

Okay! Many thanks for that! Of course, it very much complicates the picture, and I'm very puzzled as to how the Fuel Cutoff Switches and Valves operate. Apparently, the TCAM system shuts off an errant engine on the ground at least, but my concern is not with the software but the hardware. It obviously has an Output going into the Fuel Shutoff system. If the TCAM unit loses power, can that output cause the Cutoff process (powered by the engine-dedicated generator) to be activated? I guess that's the $64 billion question, but if MCAS is any example, then: Probably!

Originally Posted by BrogulT

I keep reading this theory and I'm baffled. You think the PF is going to attempt a dual engine shutoff and relight during the initial climb based on a hunch that the engines have quit, all without even a sideways glance to see what N1 is or a short word with the PM?

Originally Posted by MaybeItIs

Ok, thanks for clarifying. Of course, an overload will simply cause the hydraulic pressure relief valves to activate. There will be a moderate increase in motor current when bypassing, but the electrical side should be fully able to cope with that. Should be! I'm suggesting here that there was a fault somewhere in the electrical supplies that effectively derated some part of it, and that maybe the GearUp load was too much for it on this occasion.

Originally Posted by tdracer

I don't think this test is ever done during normal operations or maintenance (at least not on purpose) as it is very abusive to the engine driven fuel pump - the sort of cavitation that this causes rapidly erodes the pumping surfaces (it's SOP to replace the engine driven fuel pump after such a test).

Originally Posted by BrogulT

In that case, I would think that it is not beyond the realm of remote possibility that for whatever reason there might be at least some of these in the field that will not actually function in the suction mode. And if we are talking about simultaneous dual-flameouts then we're already in the "realm of remote possibility", so they should be looking at these unlikely causes. If they're never tested, it's simply an unknown. Discussions so far just assume that this feature works. From what you say it would not be simple to test all of the in-service engines since the test itself is destructive. Perhaps there is some way to test without grinding up the pumps.

Originally Posted by Icarus2001

No evidence of engine failure

No evidence of RAT deployment from a poor image.

No evidence of electrical failure.

The teams of lawyers in the UK representing 53 grieving families will be working over the weekend to sign up said families to a class action.

​​​​​​​This is going to get messy.
​​​​​​​

Originally Posted by tdracer

The engine driven fuel pumps are regularly removed and overhauled - usually when the engines go through overhaul (somewhere in the 10-20,000 hour range). The results of these overhauls are monitored, and if there is evidence of unusual deterioration, etc., that will be reflected in the recommended maintenance/overhaul intervals (BTW, this is SOP for virtually every system on the aircraft, regardless of Boeing, Airbus, etc.).
The portion of the engine driven fuel pump that is subject to wear is the high-pressure gear pump - and excessive deterioration will become apparent in the inability to reach max TO thrust. The centrifugal pump (that part responsible for the suction feed) is relatively lightly loaded and seldom experiences excessive wear or deterioration - even when exposed to severe suction feed events.
As I've posted several times, in this business you 'never say never' - but the chances that both engines fuel pumps were deteriorated to the point where they could not adequately provide suction feed fuel to keep the engines running is very, very remote.

Originally Posted by aeo

So are we now saying total loss of AC power for the RAT activation and activation of TCMA on two very independent engines for the power loss? What are the chances..

I can buy the AC power loss, but TCMA activation as well - That\x92s a stretch. TCMA is available on the ground and on approach and will activate if the engine thrust doesn\x92t follow the Thrust Lever command. On the ground it will shut the engine down (think RTO with engine stuck at T/O). On approach it will reduce the thrust if the engine doesn\x92t respond to the Thrust Lever command ala Cathay Pacific A330 (CMB - HKG) with the fuel contamination incident.

Originally Posted by tdracer

I hate to disappoint you, but the people (like me) who design, test, and certify aircraft are not idiots. We design for failures. Yes, on rare occasion, something gets missed (e.g. MCAS), but we know that aircraft power systems sometimes fail (or suffer short term interuptions) and we design for that. EVERY VALVE IN THE FUEL SYSTEM MUST BE POWERED TO CHANGE STATE!!!! If electrical power is lost, they just stay where they are. The engine fuel valve must be powered open, and it must be powered closed. Same with the spar valve. The pilot moves a switch, that provides electrical signals to the spar valve and the engine fuel valve to open or close. It's not complicated and has been in use for decades.
TCMA (not TCAM) - Thrust Control Malfunction Accommodation - is a FADEC based system. It's resident in the engine FADEC (aka EEC) - the ONLY inputs from the aircraft that go into the TCMA is air/ground (to enable) and thrust lever position (to determine if the engine is doing what it's being commanded to do. The FADEC has the ability to shutdown the engine via the N2 overspeed protection system - this is separate from the aircraft run/cutoff signal, although it uses the same HPSOV to effect the shutdown. That same system is used by TCMA to shutoff fuel if it determines the engine is 'running away'.

Hint, you might try going back a few pages and reading where all this has been posted previously.

Originally Posted by bakutteh

Do not discount the mistaken early flap retraction scenario too easily. Mull on this:

PF commanded gear up on attaining positive rate of climb, fixating on the HUD.
PM mistakenly raise flap lever from 5 to Flap 1 gate. Thrust reduced to Climb Thrust. Landing gear remained deployed. Massive loss of lift misidentified as loss of thrust. If any one pilot just had a dual engine failure scenario on a recent sim ride, brain and muscle memory would jump to loss of thrust in dual engine, prompting them to accomplish the recall memory items which called for both engine fuel switches to OFF and then RUN, and physically deployed the RAT.

There would be immediate loss of thrust with the engine taking time to recover , if at all, at such low airspeed!
The rest is left for Ppruners’ imagination.😖🥴😬